Wind induced reverse flow and vertical profile characteristics in a semi-enclosed bay of large shallow Lake Taihu, China

Abstract

Wind controls the movement of water in large shallow lakes. It ultimately affects the water quality of large shallow lakes through sediment resuspension and nutrient diffusion. Impacts of the wind field, hence needed to be studied, especially; (1) the impacts of wind field on the vertical profile, and (2) on the generation of the reverse flow field at large shallow wind exposed lakes. The present study investigated the wind field impacts on the water flow field at different water depths in the large shallow Taihu Lake by using precise wind and velocity profile data acquired at Dongtaihu bay. The results revealed that wind speed and direction have dominant effects on water movement in the large shallow lake. High frequency of wind direction generates more frequent reverse flow field at each layer of the water column. The dominant wind directions found with a high probability of contribution in the generation of reverse flows at the surface (42.4%), upper middle (38.4%) and bottom (51.5%) layers with large-scale shear of the flow field. Similarly, probability statistics showed that dominant wind speeds have more contributions in the generation of compensation currents at the lower middle (42.6%) layer of the vertical water profile with medium scale shear of the flow field. High wind speeds play a major role in the generation of large flows at all layers of flow profile, but long-term steady wind speeds with consistent wind direction generate stable current in the large shallow lake which reduce the diffusion and nutrient resuspension in the large shallow Taihu Lake. Results of the current study provide a novel ground to study sediment/nutrient resuspension, transport and water quality scenarios in large shallow wind exposed lakes while considering reverse flow field in shallow waters.